Yep, OSB, MDF, particle board and similar bottom of the barrel stuff is something to avoid.
Plywood and timber/timber (natural, not engineered wood) are pretty the only types of wood we use.
Particle boards just fall apart and break.
As for nails, I'm pretty confident we don't have a single nail anywhere on our layout, and certainly none used for construction.

Hmm, apparently we talk about different bendings. We took one whole sheet of plywood (170 x 240 cm) and cut out a 20 cm (enough for two tracks) wide oval out of it in the shape of the spiral viewed from the top. Then we cut the oval in one spot and lifted one side of the cut by 10 cm to meet the next layer of the spiral. That's all the bending we did.

They take up less space, so more stuff!
Also, they can run upside down, but I'm not sure why would that be a significant plus.
Uh, let me tell you my experience with thin plywood. Just for reference, we use ceiba plywood pretty much exclusively for our layout, including for this part. Your pine may differ slightly, but I wouldn't expect major differences.
We have three spirals on the layout. When we started working on the first one, we started from the level that goes from 10 cm below floor and slowly climbs to about 60 cm above floor where the spiral starts. In order to achieve compactness, the idea we had was to use two sheets of 4 mm ply cut in segments and glued and stacked like bricks, so the finished product would be one single piece. We would place one sheet, spread the glue, place the other sheet over it with half of the second sheet overhanging so it connects with the next segment on the lower layer. The sheets were stapled together to hold them until the glue dries. Everything went well so we prepared a whole lot of plywood, cut them to size and stacked them in a corner so we can just take the next piece without needing to stop the work to cut some more. We made various jigs for the table saw and jigsaw and prepared enough plywood for roughly entire spiral that goes from 60 cm to about 320 cm (some 25 turns, each about 4,5 m in circumference, double track).
So, place a sheet, spread the glue, place another sheet, staple, repeat. Sounds simple enough and it was, while we were working on the floor level. The horror story starts as soon we started to climb above the floor. No amount of staples, clamps and supports we could throw at the thing managed to keep it together. It was bending at the joints and delaminating all around. It was too flimsy and bending horribly. The glue wasn't drying nearly fast enough and staples didn't hold.
So, we ripped it all apart, and went back to 10 mm plywood. The first two spirals were done with it, no major issues any more.
Fast forward 3 years, we still have a whole bunch of 4 mm plywood precut into perfectly nice 90 degree circle segments sitting in the storage and the next project to do is the third and final spiral. So, in order to save some money on material, we'll use that plywood, but this time we'll be smarter and glue up the pieces before trying to install them and not even entertain the idea of one continuous piece made by gluing pieces in brick like formation. We'll just use the 90 degree segments glued in pairs for combined 8 mm and connect them with iron plates (the method we used on previous two spirals, but with single 10 mm ply). We glued all that up, let it dry for a week or so and went to work. We finished the entire spiral, 11 turns, if I remember correctly, did all the wiring (about 100 feedback sensors, some 20 turnouts and power wires on each turn). Each layer ended up being an oval composed of four 90 degree turns (two adjacent on each end), and one 30-ish cm long straight segment in the middle on two long sides.
It was not good. The plywood was still too flexible and flimsy. Even with metal bracing vertically connecting all the layers every 30-50 cm it was not rigid enough. We've spent about half a year fixing and mending the damned thing, adding additional reinforcements, but the trains kept on derailing.
So we decided to fix it once and for all. We bought 15 or so sheets of 15 mm plywood and disassembled the entire thing. Me and one colleague were working on disassembling, keeping track of all the wires and track pieces (very important XD), while three others were taking the disassembled layers, tracing them on new plywood sheets and cutting them out. For added rigidity, we cut out entire one turn from a single sheet, with all the exterior branches we could fit on each sheet. Once the entire old spiral was out, we started putting in the new wood. 15 mm proved to be bendable enough, we had no problem with it not cooperating.
It took us about two weeks, but it was probably the best thing we decided to do with it.
As for the 4 mm plywood, the pieces that were used on the spiral went to trash, but we still have a pile of unused precut segments. It's been about 6 years since we cut them.
I still hate them.
Don't use thin plywood.

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I don't understand why they would think that the HULK SMASH!! approach would be better than some bunker buster munition, which can penetrate around 5 m of reinforced concrete and be dropped from a plane or rocket launched from miles away.
Faster, cheaper, easier to deploy, more likely to do the job, proven tech.
Neural-shmeural link.

That is such a long time.
Anyway, early bases have little to marginal shielding.
Next generation of facilities, if/when the need for longer stays emerges, gets better protection, why not a bunker.
If/when those bases become lifetime colonies, then we can start thinking of shielding the entire thing. The concept is the same with camping. If you intend to stay more than a few days, you'll be looking at ways to improve your camp, but if it's just for one night, you won't bother with setting up a running water system, flush toilet, or a perimeter fence.

Schwerer Gustav says "Hi!".
It was 7.1 m wide and rode on two parallel tracks. I'm not sure exactly how wide those tracks were spaced out, but I'd presume just under those 7.1 m would be a safe guess. Sure, not a single gauge, but still...
Joking aside, yes broadest gauge is around 7 feet (2410 mm), but in any case, train wheels don't slip in curves. Wheels are slightly conical with wider part near the flange. In a curve the wheels move slightly outwards from the center line, which means that the outer wheel suddenly has a larger circumference than the inner, which leads to the wheels properly following the curve without slipping and sliding.